Water-in-oil emulsion explosive compositions utilizing solid particulate ammonium nitrate ("AN") are known in the explosives industry. See U.S. Pat. Nos. 4,555,278; 4,111,727; and 4,181,546. Explosives consisting of a water-in-oil emulsion and oxidizer salt prills are known as "blended explosives" and have a high bulk density, good blasting energy and good water resistance. However, disadvantages involved in the use of blended explosives having particulate oxidizer salt relate to the blend's pumpability and stability. More importantly, the blend's stability relates directly to the explosive properties of the blend. Some known blends are difficult to handle, i.e., to pump or auger. Further, some blends must be handled immediately after blending because over a short period of time the emulsion destabilizes ("breaks") and becomes hard, thus making the blend unpumpable and undetonable. This is especially true for certain blended emulsions using prills having a particular type of internal additive. Specifically, prills having an internal additive of a naphthalene sulfonate surfactant present stability problems when used with blended explosives utilizing a certain type of emulsifier.
Derivatives of polyisobutylene succinic anhydride are known in the art as good water-in-oil emulsifiers. Specifically, water-in-oil emulsions utilizing derivatives of polyisobutylene succinic anhydride ("PIBSA") as an emulsifier exhibit good stability and are disclosed in U.S. Pat. Nos. 4,357,184; 4,708,753; 4,784,706; 4,822,433; 4,828,633; 4,820,361 and E.P. No. 0 331 430. Atlas Powder of Tamaqua, Pennsylvania, produces water-in-oil emulsions utilizing PIBSA derivatives as emulsifiers and sells them under the tradenames APEX.RTM. and POWERMAX.RTM..
To obtain sufficient detonation velocity, it is important to provide a readily deliverable oxygen source in the explosive composition. Oxidizer salts are the most widely used source of readily deliverable oxygen for explosive compositions. For example, ammonium nitrate is a common oxidizer salt used in the industry. Ammonium nitrate is made from anhydrous ammonium and nitric acid, and is produced in forms ranging from crystals to porous agglomerates known as prills. The present invention is directed to blended explosive compositions utilizing oxidizer salts in prill form. Generally, oxidizer salt prills used in blended explosives are made by spraying a solution of the salt against a countercurrent stream of air in a prilling tower. Particles of the oxidizer salt are formed. These particles are dried and then coated to improve flow characteristics and moisture resistance. Not only have prill coatings been applied after the prill is formed, but prills have also been developed which include internal additives used during the prilling process to produce a high-quality prill. See U.S. Pat. No. 4,749,349 to Kaltenbach-Thuring, S.A.
Typical external coatings for prills are binary, that is, one chemical is used to help a second chemical adhere to the surface of the prill. For example, usually an organic surfactant is used to help clay or talc adhere to the prill. The clay or talc acts as a "parting agent" and/or "anti-caking agent" to reduce caking and clumping of the prills. Caking and clumping of prills before blending with the emulsion is a common problem in the explosives industry and it occurs more frequently in the summer months during high humidity conditions.
Organic surfactants are known in the industry as coatings for prills so that clay or talc can adhere thereto. See EP 8900923.2. For example, such an organic surfactant in the general chemical class of naphthalene sulfonates is sold under the trade name GALORYL AT 4045 by Lobeco Products, Inc. of Beaufort, S.C. to help clay or talc adhere to prills. GALORYL AT 4045 has a specific gravity of 1.110 (water =1), is soluble in water, has a boiling point of 212.degree. F., melting point, i.e., liquid freezes at 32.degree. F., a vapor pressure of 17.5 mmHg (at 20.degree. C.), and a vapor density of 0.6 (air =1).
The recent introduction of prills made by the Kaltenbach-Thuring process, U.S. Pat. No. 4,749,349 ("KT prills"), which include an internal additive of a naphthalene sulfonate surfactant and an external coating of a naphthalene sulfonate surfactant have caused stability problems in blends of this particular prill and certain water-in-oil emulsions.
A prill having an internal additive of a naphthalene sulfonate surfactant and an external coating of a naphthalene sulfonate surfactant produces a prill of good quality having low moisture content and low fines content. Further, the use of a naphthalene sulfonate surfactant during the prilling process not only provides a prill of high quality but reduces production costs substantially. Due to the above qualities, these prills represent an advancement over other prills known in the art. However, it has been found that these prills which include a naphthalene sulfonate surfactant destabilize blended emulsions which utilize derivatives of polyisobutylene succinic anhydride ("PIBSA-type") as an emulsifier. Specifically, the naphthalene sulfonate surfactant of the prill interferes with the water-in-oil emulsion structure and causes the emulsion to break, thus making the emulsion difficult to handle. Further, as a result of the interference, the blend may not be detonable. While removing the external coating of the prill improves the stability of the blended emulsion it does not provide a practical solution since the uncoated prills cake making it difficult, if not impossible, to blend the prills with the water-in-oil emulsion.
Therefore, there is a need to provide a coating for prills having a naphthalene sulfonate surfactant as an internal additive which is compatible with blended explosive compositions utilizing derivatives of polyisobutylene succinic anhydride as an emulsifier.